Addiction and other neuropsychiatric diseases involve altered learning and decision-making. The mechanism of these alterations, the circuits affected, and their significance to behavior are not well understood. We are using an animal models of addiction, associative learning and decision making to study the neural circuits mediating simple associative learning and decision-making and to identify critical changes that may underlie addiction and other co-morbid neuropsychiatric disorders. It is hoped that by better understanding these changes, we will have better models for intervention.